Electric-arc cutting



P. P. ALEXANDER I 1,746,203

. ELECTRIC ARC CUTTING Original Filed Aug. 26, 1925 Inventor Peter PAlexandef,

His Attorhgy.

Patented Feb. 4, 1930 UNITED STATES PATENT OFFICE PETER I. ALEXANDER, OFMARBLEHEAD, MASSACHUSETTS, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A.CORPORATION OF NEW YORK ELECTRIC-ARC CUTTING Application filed August26, 1925, Serial No. 52,663. Renewed October 3, 1927.

My invention relates to the cutting of metals by means of the electricare.

An object of my invention is to provide an improved process and animproved apparatus utilizing an arc of relatively high potential andgreat heating capacity to cut metals. Although not limited thereto myinvention finds particular application to the cutting of cast iron andnon-ferrous metals.

The are voltage using a carbon electrode in air is on the average of 37volts and the current values used are high, in some cases as high as1500 amperes. The width of the groove cut depends on the size of theelectrode which in turn depends on the value of the current used. As thecutting is essentially a melting process the speed is determined by theamount of metal to be removed and the energy supplied for that purpose.

As pointed out in my application, Serial No. 758,082, filed December 26,1924, for methods and apparatus for electric arc welding, and assignedto the same assignee as the present application, the voltage of the arcin a hydrogen atmosphere is greatly in excess of that of thecorresponding are in air. The

high normal voltage of such an arc makes it possible to secure a muchgreater heating effect with this are in the hydrogen atmosphere than inair for the same current and with this high are voltage and a highcurrent value the energy available by the employment of such an arc istre nndous. Furthermore, the are in hydrogen has its largest fall ofpotential in the gaseous layer next to the positive crater; that is alarge proportion of the energy is produced at the exact place Where itis needed when the work to be cut is made the positive side of thecircuit.

, Because of the high voltage great energy may be derived with lowcurrent values and thus one generator may be used both for welding andcutting. If the necessary high striking voltageof about 120 voltsfor an31011 1 a hydrogen atmosphere be obtained by the 1nsertion of a properlypredetermined reactance in the circuit any suitable source of currentmay be used, for example a enerator such as shown in Letters Patent toergman, No. 1,340,004 wound for about 80 volts on open circuit has beenfound to give satisfactory operation. The minimum arc voltage inhydrogen is about 40 volts, but it is to be understood that are voltagesgreatly in excess of this may be used where a suitable supply circuit isused. The arc voltage depends upon the arc length. I have successfullyused are voltages in excess of 7 5 volts and higher voltages may be usedif desired.

My invention is to be distinguished from cutting arrangements andprocesses wherein the heating effect of an arc is supplemented by thechemical reaction of combustion of gases such for example as oxygen andhydro gen. In accordance with my invention the gaseous medium is notoxidizing but actively reducing in its nature. The gas need be suppliedin relatively small quantities. The method of cutting may be such as toallow a free flow of the melted metal from the cut or section butpreferably the gaseous medium is supplied in the form of a blast whichremoves the molten metal.

The cost of hydrogen per cubic foot is at the present time from two andone half to three times lower than that of oxygen or acetylene. In largeindustrial plants hydrogen is available as a by-product. In such a caseits cost is only one twentieth that of acetylene. Tlie reducing gaseousmediumneed not be pure hydrogen but I deem it preferable to use a mediumwhich contains or is decomposed in the arc to produce a considerablepercentage of hydrogen. For example, I have found illuminating gas maybe used. Illuminating gas contains around 30 to 40% of hydrogen and asomewhat smaller amount of carbon monoxide. The hydrocarbons and carbondioxide of illuminating gas are decom osed and recombined when the arcis con ned in the kerf with the further liberatron of hydrogen. Thepresence of carbon monoxide in substantial proportions tends to cost ofmy gas are cutting process using il1uminating'gas will be comparable toor lower than that of the previous gas cutting means and it is much moresatisfactory for cast iron and non-ferrous metals. 7

By my process I have cut cast iron and steel plates of one and twoinches in thickness with. a current of 130 amperes; at speeds of 30 and40 feet per hour and the edges of the cuts have been clean and sharp andcompare favorably with the cuts made with the oxy-hy: drogen torch. Thereducing gas flame protects the metal during the operation and the edgesare not oxidized as is the case in oxyhydrogen or oxy-ace'tylene cuttingwhere the basic principle of the process rests upon the oxidization andburning of the metal. Furthermore, since the gas flame entirelysurrounds the electrode its consumption is greatly lessened.

Aside from these advantagesof low cost 'ofoperation, the possibility ofusing a single standard generator as above pointed out for both weldingand cutting purposes 1s a great advantage. Atthe present time cutting.by the carbon arc necessitates machines capable of developing from 600to 1000 amperes or more.-

The single figure of the drawing illustrates an automatic machine for.carrying out my invention. In the figure, 10 is a graphite or carbonelectrode which is mounted insliding engagement within a tube 11 locatedin the face of the nozzle 12. The electrode 10 may be adjusted in thetube 11 by means of a screw 13. The end of the tube 11 is enameled toprevent accidental short circuiting of the arc when the electrode is ina deep narrow cut.

A heavy copper tube 14 conducts the gas and the current simultaneouslyto the nozzle 12. Gas is supplied to the tube by a pipe 15 and oneterminal of the source of welding current is connected at 16 to thistube. Tube 14 slides in the steel block 17 so that the height of theelectrode above the work can be adjusted. The block 17 slides freelywithin a sleeve 18 which is supported by a carriage 19. Block 17 is alsoprovided with arms 20 carrying at their extremities cam followers 21.These cam followers are forced into engagement'by gravity with cams 22adjustably located by means of splined joints to axles 23 of thecarriage 19.

' The carriage 19 is arranged to move on rack rails 24 and is positiveldriven by a motor 25 mounted on a brac et 26- secured to the carriage bya gear train 27 which drivesone of the axles of the carriage. The motor25 may be a constant speed motor or as shown in the drawing it may haveits terminals connected across the arc in which case the speed ofcutting will be regulated automatically. If the arc length is shprtenedby the metal not being removed at a rate corresponding to the speed ofpropulsion of the move more metal.

carriage the voltage impressedon motor 23 will be lessened and thecarriage slowed in its travel so that the energy in the arc may re--len' 'th which is determined by the rate of re- 11103211 of metal. a

As the motor advances the carriage along the rack rails the rotarymovement of the earns 22 secured to the axles 23 of the carriage causesthe block 17 by means of arms 20 and the cam followers 21 to oscillatethereby oscillating the electrode vertically in the plane of the kerf.

lVhen operating the machine it is preferable to keep the arc between theelectrode 10 and the work 28 within the kerf, since if the are bebrought to the surface of the work there is a tendency for it to wanderabout over the surface of the Work and produce a rough and irregularkerf.

The application of Irving Langmuir, Serial No. 7 29,185, filed July 30,1924:, for heating process and apparatus, assigned to the same assigneeas the present application, discloses and claims method and apparatusfor producing atomic hydrogen and carrying it over to the work Where itis recombined, lib crating heat. WVhether or not heating of the work bythe recombination of dissociated hydrogen may under certaincircumstances be present to some extent when my invention is used, Imake no claim to such subject matter since the Langmuir invention isearlier than my invention.

While I have described and illustrated an apparatus particularly adaptedfor carrying out my process where a certain class of work is to be cut,it is apparent that for many classes of work a hand tool maybepreferable. It will also be apparent to those skilled in the art that asfar as the broader aspects of my apparatus are concerned it isimmaterial whether the machineoperates on rails over the work or rollsdirectly upon the work or remains stationary While the Work moves. Itherefore, aim in the appended claims to cover all such modificationsand constituting the other electrode and supply ing a blast of areducing gaseous medium containing hydrogen to envelop the are andremove the molten metal.

2. The method of cutting metal work by the electric are which comprisesmaintaining a cutting are within the kerf in the work between a negativeelectrode and the work constituting the positive electrode and supplyinga blast of illuminating gas to envelop the arc and remove molten metal.

3. A gas are cutting machine wherein the arc is between an electrode andthe work, comprising means for producing relative movement between thearc and the work along the section to be cut, means for oscillating. theelectrode in the plane of the cut, and means for supplying a blast ofgaseous medium to envelop the arc and remove molten metal.

4. A gas are cutting machine wherein the arc is between an electrode andthe work, comprising means for producing relative movement between thearc and the work along the section-to be cut, means for oscillating theelectrode in the plane of the cut and within the kerf, means forsupplying a blast of gaseous medium to envelop the arc and remove moltenmetal, and means for controlling the rate of movement along the work inresponse to an electrical characteristic of the are which varies withthe arc length.

5. A gas are cutting device comprising a gas delivery nozzle, anelectrode mounted in said nozzle, a support for said nozzle, and meansfor vertically oscillating said nozzle relatively to the work.

6. An are cutting machine wherein an arc is maintained between asubstantially non-consuming electrode and the work comprising means forproducing relative movement between the arc and the work along thesection to be cut, means for oscillating the electrode in the plane ofthe cut, and means for controlling the rate of movement along the workin response to an electrical characteristic of the are which varies withthe arc length.

7. The method of cutting metals by the electric arc which comprisesmaintaining a cutting are between a negative electrode and the workconstituting the positive eletrode and supplying a reducing gaseousmedium containing hydrogen about the arc and molten metal.

In witness whereof I have hereunto set my hand this 12th day of August,1925.

PETER P. ALEXANDER.

